MALE GENITAL SYSTEM: INTERNAL ORGANS 



37i 



processes and the bodies of the vertebrae. Against its extensive surface lie the kidneys 

 and the generative tract, the intestine and rectum and the aorta and postcavae, which 

 are interposed between the muscle masses of opposite sides. In the lumbar and pedi- 

 cular region the hypaxial muscle is divided into two tracts — a deep portion against the 

 bodies of the vertebrae and the transverse processes, and a superficial portion more 

 ventrally abutting on the hypapophyses of the vertebrae. 



The transversarius muscle occupies the region of the transverse processes laterally. 

 For its origins and insertions and for further details of those of the muscles of this region 

 see Schulte, 1916, pp. 426-7. 



INTERNAL ORGANS 

 The penis 



The smooth tapering penis is enclosed as far distally as the praeputial fold by a 

 musculo-fibrous sheath (Figs. 2 e, 3 e). The muscular elements in this sheath are pro- 

 nounced proximally and form a moderately thick circular layer derived from the panni- 

 culus carnosus. Distally these muscles give place to fibres directed circularly around the 

 shaft of the organ. 



The penis may be considered to consist of two parts, an external part comprising the 

 main shaft of the organ together with the conical terminal part, and an internal portion 

 not visible externally where the shaft of the organ swells out to form the bulbus penis. 

 In the adult and later foetal life the external part is retractile into the "penis sac". 

 Although in young foetuses the "penis sac" is not developed the retractor muscles are 

 yet capable of action and, in preserved specimens at any rate, are in a state of contraction 

 causing an artificial shortening of the external part of the organ and the formation of a 

 circular collar of skin into the middle of which the terminal cone is pulled down. In the 



Fig. 1. Internal genitalia of a male Fin whale foetus 2-65 m. in length. 



