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Context 1
... Plecotus macrobullaris the medullary cavity is a wide, round canal through the whole length of the shaft except for the very tip, where it tapers toward the distal end ( Figure 3.15). At the base of the shaft, the canal widens into a junctional cavity from which two canals extend into the branches (Figures 3.12 and 3.15). In the branches, the medullary canal is oval in cross section and about twice as wide as in the shaft. ...
Context 2
... nutrient canal enters the junctional cavity approximately in the middle (nearer to the shaft) of the baculum, with a small nutritional foramen ventrally (Figure 3.13). Other canals enter the medullary cavity near the tip in each of the branches, with the foramina nutritia at the medially on the branches (Figure 3.12). ...
Citations
... In a more recent approach, our research group has already applied correlative 2D and 3Dimaging to describe baculum histomorphology in three species of the bat genus Plecotus (Herdina, 2008;Herdina et al., 2010a). As suggested at least for Plecotus, the micromorphological traits of shape and position of the medullary cavity in the baculum and the position and number of nutrient foramina (where blood vessels enter the bone from the periosteum going into Volkmann's canals) may prove useful for species discrimination (Herdina, 2008). ...
... In a more recent approach, our research group has already applied correlative 2D and 3Dimaging to describe baculum histomorphology in three species of the bat genus Plecotus (Herdina, 2008;Herdina et al., 2010a). As suggested at least for Plecotus, the micromorphological traits of shape and position of the medullary cavity in the baculum and the position and number of nutrient foramina (where blood vessels enter the bone from the periosteum going into Volkmann's canals) may prove useful for species discrimination (Herdina, 2008). Research on penis bone histomorphology could also add valuable information about the development of the baculum and its mechanical function. ...
... Differences in dorsoventral curve shape (Fig. 1), as found between the specimens of Pipistrellus pipistrellus, P. pygmaeus, and P. hanaki, seem to represent only individual variation. The location and length of the medullary canal, Volkmann's canals, and nutrient foramina in Pipistrellus pipistrellus, P. pygmaeus, P. hanaki, and P. nathusii exhibit much more individual variation than in the Plecotus species examined previously (Herdina, 2008;Herdina et al., 2010a). This variation ranges from specimens without any medullary canals to specimens with large cavities in the branches of the proximal base, and extremely large nutrient foramina. ...
Detailed knowledge of histomorphology is a prerequisite for the understanding of function, variation, and development. In bats, as in other mammals, penis and baculum morphology are important in species discrimination and phylogenetic studies. In this study, nondestructive 3D-microtomographic (microCT, µCT) images of bacula and iodine-stained penes of Pipistrellus pipistrellus were correlated with light microscopic images from undecalcified surface-stained ground sections of three of these penes of P. pipistrellus (1 juvenile). The results were then compared with µCT-images of bacula of P. pygmaeus, P. hanaki, and P. nathusii. The Y-shaped baculum in all studied Pipistrellus species has a proximal base with two club-shaped branches, a long slender shaft, and a forked distal tip. The branches contain a medullary cavity of variable size, which tapers into a central canal of variable length in the proximal baculum shaft. Both are surrounded by a lamellar and a woven bone layer and contain fatty marrow and blood vessels. The distal shaft consists of woven bone only, without a vascular canal. The proximal ends of the branches are connected with the tunica albuginea of the corpora cavernosa via entheses. In the penis shaft, the corpus spongiosum-surrounded urethra lies in a ventral grove of the corpora cavernosa, and continues in the glans under the baculum. The glans penis predominantly comprises an enlarged corpus spongiosum, which surrounds urethra and baculum. In the 12 studied juvenile and subadult P. pipistrellus specimens the proximal branches of the baculum were shorter and without marrow cavity, while shaft and distal tip appeared already fully developed. The present combination with light microscopic images from one species enabled a more reliable interpretation of histomorphological structures in the µCT-images from all four Pipistrellus species. J. Morphol., 2015. © 2015 Wiley Periodicals, Inc.
© 2015 Wiley Periodicals, Inc.
... From the three-dimensional (3D) images of this study, we can confirm that the proximal end of the baculum is linked to the corpora cavernosa over a much larger area than we previously thought (Herdina et al. 2010): not only the very end is connected, but also a broad area of the dorsal surface all along the bifurcated part of the proximal base of the baculum (see Herdina, 2008;Herdina et al. 2014b). ...
... From our previous histological studies, we know the baculum is tightly linked to the corpora cavernosa via entheses. The tunica albuginea merges into the periosteum of the baculum without a histologically distinguishable border between the tissues (Herdina, 2008;Herdina et al. 2010Herdina et al. , 2014b. Thus when the corpora cavernosa expand and stiffen, the baculum is pulled into a straight line with the corpora cavernosa in N. noctula and P. pipistrellus, or into an angle with the tip pointing dorsally in P. nathusii, moving the distal tip up dorsally and pulling the proximal end down (Figs 3-5, white arrows). ...
... The baculum is directly dorsal to the part of the urethra that goes through the glans, and the distal forked tip of the baculum surrounds the dorsal half of the urethral opening ( Fig. 6; Herdina, 2008;Herdina et al. 2010Herdina et al. , 2014b. One hypothesized function of the baculum is that it protects the distal urethra and urethral opening from compression during erection and copulation (Dixson, 1995). ...
The baculum (os penis) has been extensively studied as a taxon-specific character in bats and other mammals but its mechanical function is still unclear. There is a wide consensus in the literature that the baculum is probably a sexually selected character. Using a novel approach combining postmortem manipulation and three-dimensional (3D) imaging, we tested two functional hypotheses in the common noctule bat Nyctalus noctula, the common pipistrelle Pipistrellus pipistrellus, and Nathusius' pipistrelle Pipistrellus nathusii: (i) whether the baculum can protect the distal urethra and urethral opening from compression during erection and copulation; and (ii) whether the baculum and corpora cavernosa form a functional unit to support both the penile shaft and the more distal glans tip. In freshly dead or frozen and thawed bats, we compared flaccid penises with artificially 'erect' penises that were inflated with 10% formalin. Penises were stained with alcoholic iodine and imaged with a lab-based high-resolution x-ray microtomography system. Analysis of the 3D images enabled us to compare the changes in relative positions of the baculum, corpora cavernosa, urethra, and corpus spongiosum with one another between flaccid and 'erect' penises. Our results support both functional hypotheses, indicating that the baculum probably performs two different roles during erection. Our approach should prove valuable for comparing and testing the functions of different baculum morphologies in bats and other mammals. Moreover, we have validated an essential component of the groundwork necessary to extend this approach with finite element analysis for quantitative 3D biomechanical modeling of penis function.
© 2015 Anatomical Society.
... The base of the baculum usually consists of two branches, whose proximal ends are linked closely to the corpora cavernosa. The tunica albuginea of both corpora cavernosa continues into the periosteum of the baculum [Matthews, 1937;Topál, 1958;Herdina, 2008;]. ...
... Each of those forms could later be assigned to a separate Plecotus species . There are also micromorphological traits, like position and shape of the medullary cavity, that might be useful for species identification in some genera [Herdina, 2008;. ...
... This study confirms that macroscopic details and dimensions along with histomorphology of the baculum can be used for bat species identification. Both these methods have been successfully applied to differentiate Plecotus austriacus, P. auritus and P. macrobullaris (Herdina, 2008). ...
With the recent discovery of many cryptic bat species, finding morphological characters
discriminating these genetically defined taxa has become a crucial issue. The baculum
(os penis) has been assumed to play a role in mate choice and could be a mating barrier
between closely related species. Thus, it has been used in species discrimination for a long
time. The Pipistrellus pipistrellus/pygmaeus species complex is a model system for cryptic
diversity in European bats. However, no reliable morphological discriminating characters
have yet been found. This dissertation introduces a discriminant function, combining
projected length, width, and height of the baculum, which was able to reliably assign
97.9% of the tested specimens (n=48) to their genetically identified species. To establish a
baseline for functional anatomy, the baculum was studied histologically and experimentally.
The baculum in connection with the surrounding soft tissues of the penis in Plecotus and
Pipistrellus species was evaluated in serial, surface-stained ground sections and semithin
sections in combination with microCT imaging. To test hypotheses on baculum function
experimentally, the corpora cavernosa of bat penes were inflated post mortem. Baculum
positions in relation to the soft tissues were compared in high-resolution microCT virtual
sections and 3D models of flaccid and "erect" penes. Histomorphological and experimental
results supported both of the hypotheses tested: 1) baculum and corpora cavernosa form
a functional unit, supporting both the penile shaft and the glans; and 2) the baculum
can protect the distal urethra and urethral opening from compression during erection and
copulation.
... This study confirms that macroscopic details and dimensions along with histomorphology of the baculum can be used for bat species identification. Both these methods have been successfully applied to differentiate Plecotus austriacus, P. auritus and P. macrobullaris ( Herdina, 2008). Future work with these techniques on larger sample sizes in a greater number of species will also provide more insight into potential intraspecific variation in bacular microanatomy. ...
For the first time, the histomorphology of the penis bone of a bat (Plecotus austriacus) was examined in detail. From Plecotus austriacus, 14 whole penes and 11 isolated bacula were studied and compared to bacula of Plecotus auritus and Plecotus macrobullaris. The baculum was located on specimen microradiographs and in micro-CT images in the tip of the penis. Using serial semithin sections and surface-stained, undecalcified ground sections, the types of bone and other tissues constituting the baculum were examined by light microscopy. 3D reconstructions were generated from the serial semithin sections and from micro-CT images. The shaft and the proximal branches of the Y-shaped baculum form a tubular bone around a medullary cavity. Since the small diameter of this channel and the main lamellar bone around it resemble a Haversian canal, the baculum is equivalent to a single-osteon bone. Several oblique nutrient canals enter this medullary cavity in the shaft and branches. All ends of the baculum consist predominantly of woven bone. The collagen fiber bundles of the tunica albuginea of both corpora cavernosa insert via fibrocartilage into the woven bone of the branches. Thus, the microscopic structures support the hypothesis that the baculum functions as a stiffening element in the erect penis. In this study, several microscopic imaging techniques were evaluated for displaying the microscopic structures of the baculum. Specimen microradiography, but especially micro-CT proved to be suitable nondestructive methods for accurate and reproducible demonstration and comparison of the three-dimensional structures of the baculum in different bat species.
