318 THE ANATOMY OF VERTEBRATED ANIMALS. 



In the male, the penis is contained in a long prepuce, and, 

 like that of the Horse, is devoid of a bone and provided with 

 retractor muscles. The prostate is lobed. There is a large 

 uterus masculinus and well-developed vesiculas seminales. 

 The ducts of Cowper's glands open into a c£ecal cavity con- 

 tained in the muscular balb. The testes descend into a scro- 

 tum. In the Sow, a pair of Gaertner's canals^ or persistent 

 Wolffian ducts, open into the vestibule beside the urinary 

 meatus. The uterine cornua are very long, and the ovaries 

 are lobulated. The period of gestation is sixteen to twenty 

 weeks. The ovum, at first spherical, retains that form until it 

 attains a diameter of nearly half an inch. It then rapidly 

 elongates into a coiled filiform body, as much as twenty inches 

 long. Both the allantois and the umbilical vesicle at the same 

 time assume a spindle-shape. 



The allantois soon becomes divided into an internal epithe- 

 lial and an external vascular layer ; the latter becoming united 

 with the chorion, through the extremities of w^iich the allan- 

 tois eventually passes. The villi are very numerous, minute, 

 and spread over the whole surface of the ovum. 



The Suidce exhibit great variations in their dentition and 

 in the structure of the stomach. 



In JPoTCiis (the Babyrussa) the dental formula is ^. ^3 c. jfj 

 p.m.in, g-^ ; the canines are enormously elongated and recurved, 



and the pharynx is provided with peculiar air-sacs. 



The stomach is divided into three chambers, and the groove 

 leading from the oesophagus toward the pylorus is more dis- 

 tinctly marked than in the S>us. 



In JDlcotyles (the Peccaries) the upper incisors are also 

 reduced to two on each side, and the molar teeth present 

 transverse ridges, which are more distinct and less tuberculated 

 than in Sus. 



The stomach is divided into three sacs, and is provided 

 with an oesophageal groove as in the preceding genus. 



The middle metatarsals and metacarpals coalesce into a 

 cannon-bone, and the fifth digit of the pes is represented only 

 by its metatarsal. 



In PJiacochcerus (the Wart-hog) the upper incisors are 

 reduced to one pair, and the hindermost molars, which are the 

 only ones which are not shed in the old animal, are of great 

 size, and possess a complicated, tuberculated structure. 



The Suidce are represented by one genus or another in ali 



