MARSUPIAL REPRODUCTION 



561 



pouch by the mother with her tongue. They become attached to the 

 teats and remain for a long time in the pouch. 



This is not by any means a primitive plan of development, it 

 involves many specializations. To make the journey to the pouch the 

 fore-limbs and their nervous centres are precociously developed, being 

 fully functional at birth, when the hind-limbs are mere buds. The 

 method of suckling also involves special developments of both mother 



Fig. 337. Phalanger sp. Female genitalia. Note caudal blind ending of the 



sinus vaginalis. 



u.h. uterine horn; s.v. sinus vaginalis; v. I. vagina lateralis; ug.s. urogenital 



sinus. (After Brass and Ottow.) 



and foetus, so that milk is injected into the latter without choking it. 

 The sides of the lips grow together round the teat, which is thrust far 

 back in the pharynx, the larynx extending forwards into the nasal 

 passage. Milk is pressed out by a special muscle (homologue of the 

 male cremaster) attached to the epipubic bones. 



The brain shows some reptilian features. The cerebral hemispheres 

 are small for a mammal, and the olfactory bulbs large. The hemi- 

 spheres are not prolonged backwards over the cerebellum, which is 

 itself small and simple. There are dorsal (hippocampal) and ventral 

 (anterior) commissures but no corpus callosum. The cochlea of the 

 ear is spirally coiled. 



