STRUCTURE OF THE PENIS. 317 



and fused with one another ; the nuclei of these cells are all 

 staff-shaped. In the middle layers, well-developed ribbed or 

 spiny cells (Biffzellen) are present, whilst the deepest cells are 

 columnar, and arranged side by side like palisades. 



The mucous membrane is rich in elastic plexuses, and pre- 

 sents also closely approximated conical and simple or divided 

 papillae, that are more distinctly developed in the adult than 

 in the newly born infant. 



The nerves of the glans are very numerous, and, according 

 to Kolliker, end within the papillae in Krause's terminal bulbs. 



The prepuce presents the same general character as the skin. 

 The epithelium of the internal lamina, however, resembles 

 laminated pavement epithelium. 



In the skin of the penis, as well as in both laminae of the 

 prepuce, sebaceous follicles are present. In the latter region 

 they are of oval form, and may have a length of 0'6 of a milli- 

 meter and a breadth of 0'35 of a millimeter. 



They extend as far as to the corona glandis, constituting the 

 glandulae Tysonianae, their size and the number of their pul- 

 lulations progressively diminishing. In the new-born infant 

 they are abundantly and well developed, both upon the in- 

 ternal and the external layer of the prepuce, whilst in some 

 adults it is difficult to establish the fact of their existence. 

 Sebaceous follicles are, as a rule, absent upon the glans penis, 

 though a few of simple form were on one occasion discovered 

 by Schweigger-Seidel at the apex of the glans. In structure 

 the sebaceous follicles of the prepuce are precisely similar to 

 those of other parts of the skin. 



In all Mammals the penis is perforated by the nrethra; amongst 

 Birds a true penis is only found in the Struthionidae and in a few 

 Gallinaceous and some Natatory Birds. 



Amongst Amphibia, Turtles possess a single, Snakes and Lizards a 

 double intromittent organ. 



The penis of Birds and Amphibia is not perforated, but simply 

 presents a groove for the discharge of the semen (Ley dig). 



Corpora cavernosa are very generally present amongst Mammals. 

 In Birds a cavernous tissue either surrounds the penis, or is found in 

 its interior (Struthio). 



