BRAIN. ALIMENTARY CANAL. GENERATIVE ORGANS. 



531 



The cerebral 



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

 sometimes be rotated on the tibia {Phascoloniyidae, Didelphyidae, Phalan- 

 geridae), and in some cases tlie first chgit can be nsed 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 miited 

 by the skin alinost to their extremities (syndactylism. Fig. 280). 

 |'*s.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 {Phascolarctus, Phas- 

 colomys). The caecuni is usually 

 present : it is large in the kangaroos, 

 small and provided with a vermi- 

 form appendix in the wombat, 

 absent in the dasyures. A gall 

 bladder is always present. 



The heart is without fossa ovalis, 

 the am'iculo-ventricular valves are 

 membranous and attached to the 

 papillary muscles by chordae tendineae, and there 



and 



the 



of 



Fig. 277.— Bifid 

 penis of Didel- 

 phys philander 

 (after Otto, 

 from Gegen- 

 baur). E the 

 two halves of 

 the glans. 



Ph 



Fig. 276.— The pelvis 



adjoining parts of 



vertebral column 



Macropus. Jl ilium ; are two superior venae cavae, each receiving an 



Pb pubis ; Js ischium ; oyvs-os vein 



M epipubic bones ; A '^^^ 8°^ ^ ^^P^' 



acetabulum ; S the two Generative organs. In the male there are no 



sacral vertebrae. 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 urinogenital 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. 278.4), 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 septmn breaks down so 

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

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

 {Macro podidae and others) the hind end of this bhnd sac acquires 

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

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

 urinogenital sinus without traversing the whole length of the vagina 

 (Fig. 278 G). 



* Brass, .\., Beitr.zur Kenntnissdesweihl. Vrorjenilal-system der Marsu- 

 pialier, Inaug. Dissert., Leipzie, 1880. Lister and Fletcher, P.Z.S., 1881, 

 p. 976. 



