BRAIN. ALIMENTARY CANAL. GENERATIVE ORGANS. 



531 



The cerebral 



they are represented bj' cartilage. The fibula is generally free, and can 

 sometimes be rotated on the tibia (Phaacolomyidae, Didelphyidae, Phalan- 

 geridae), and in some cases the first digit can be used as a thumb. The 

 pes presents considerable variation ; the tarsus contains the usual seven 

 bones, and there are usually five digits, but the hallux is frequently absent. 

 The second and third digits are in many families very slender, and united 

 by the skin almost to their extremities [syndactylism, Fig. 280). 



The brain is relatively smaller than in higher mammals. The corpus 

 callosum is absent and the anterior commissure is large. 



hemispheres vary in size and in 

 the extent to which their surface 

 is convoluted. 



The stomach is usually simple, 

 but in the kangaroos it is much 

 elongated and sacculated, like the 

 colon, by three longitudinal muscu- 

 lar bands. There is a cardiac gland 

 in some forms (Phascolarcttis, Phas- 

 colomys). The caecum is usually 

 present : it is large in the kangaroos, 

 ^A small and provided with a vermi- 

 form appendix in the wombat, 

 absent in the dasjrures. A gall 

 bladder is always present. 



The heart is without fossa ovaMs, 

 Ph the auriculo-ventricular valves are 



Fia. 276.— The pelvis and membranous and attached to the 



adjoining parts of the papiUarv muscles by chordae tendineae, and there 



vertebral column of ^ ^^ -^ . •' , . . 



are two supenor venae cavae, each receiving an 



M 



Fig. 277.— Bifid 

 penis of Didel- 

 phys philander 

 (after Otto, 

 from Gegen- 

 baur). E the 

 two halves of 

 the glans. 



Macropus. 



Jl ilium 



Pb pubis ; Js ischium ; azygos vein. 



M epipubic bones ; 

 acetabulum ; S the two 

 sacral vertebrae. 



Generative organs. In the male there are no 

 vesiculae seminales, the glans penis is frequently 

 bifurcated, the crura penis are not attached to, 

 the ischia, and the testes descend into scrotal sacs which are placed 

 in front of the penis. 



In the female * the miillerian ducts remain separate posteriorly 

 and open separately into the long m-inogenital sinus (Fig. 278.) They 

 are differentiated into oviduct, uterus and vagina on each side, and 

 the vaginal portion is curved. This is the arrangement in the simplest 

 cases (Didelphys, Fig. 278^), but in other forms the anterior part of 

 the vagina gives off a backwardly directed caecum (Fig. 278 B), which 

 is so closely applied to its fellow that it is separated from it only by a 

 median septum. In yet other forms this septum breaks down so 

 that the two vaginal caeca unite into one, the hind end of which reaches 

 back to the front end of the urinogenital sinus. In some forms 

 (Macropodidae and others) the hind end of this bUnd sac acqmres 

 at parturition, an opening into the urinogenital sinus at this point (ap- 

 parently by rupture), so that the foetus is delivered straight into the 

 urinogenital sinus without traversing the whole length of the vagina 

 (Fig. 278 G). 



* Brass A., Beitr.zur Kenntnissdeaweibl. Urogenilal-system der Marsu- 

 pialier, InLgu. Dissert., Leipzig, 1880. Lister and Fletcher P.Z.S., 1881, 

 p. 976. 



