164 TOPOGRAPHICAL ANATOMY OF THE 



small colon may lie in relation to the vertex and part of the lateral 

 surface. 



The middle part of the vertex is marked by a puckered scar, the 

 centrum verticis, which indicates the remains of the connection in the 

 embryo between the bladder and the foetal envelope known as the 

 allantois. On each side of the centrum is the termination of a liga- 

 mentum teres. 



The neck of the urinary bladder is definitely fixed in position by its 

 connection with the urethra. The rest of the organ is necessarily 

 capable of some amount of displacement, dependent upon the quantity 

 of urine contained in the sac. As has already been noted, the peritoneum 

 furnishes an unstable anchorage by its reflection from the wall of the 

 pelvis and by the formation of the middle and lateral folds or ligaments. 

 Behind the peritoneum the bladder is moored by loose connective tissue, 

 in which there is generally a considerable amount of fat. 



The prostate (Prostata). — The prostate^ of the horse is a relatively 

 large body, yellowish in colour and lobulated, lying upon the neck of the 

 bladder and the commencement of the urethra. It covers the termina- 

 tion of the deferent ducts and the narrow caudal extremity of the 

 seminal vesicles. The rectum is in contact with its dorsal surface, while 

 laterally it is separated from the wall of the pelvis by a greater or lesser 

 accumulation of fat. 



The gland is divisible into two lateral lobes (lobus dexter, lobus 

 sinister) connected by a comparatively narrow isthmus (isthmus pros- 

 tatse), over which lies a thin stratum of transverse muscular fibres (m. 

 prostaticus). The gland pours its secretion into the first part of the 

 urethra by 15 to 20 ducts (ductus prostatici). 



The deferent ducts (ductus deferentes). — The deferent ducts 

 have already been observed where they leave the other constituents of 

 the spermatic cord at the abdominal ring of the inguinal canal and turn 

 caudalwards into the pelvis. They are enclosed in the urogenital fold 

 of peritoneum, and, as they pass obliquely along the dorsal face of the 

 urinary bladder, they generally converge until they meet on the dorsal 

 surface of the neck of this sac. The last part of each duct insinuates 

 itself beneath the prostate, and finally opens, as will be seen later, into 

 the prostatic part of the urethra. 



The greater part of each duct is about 5-6 mm. in diameter ; but 

 where it is enclosed in the urogenital fold, its diameter increases to 



1 Trpoo-rdrTjj (prostates) [Gv.], one standing before (irp6, before + tffTciJ'at, to stand). 

 So named l)ecause in the human subject the gland stands before the neck of the 

 bladder. 



