250 MR. G. E. DOBSON ON CAPROMYS MELANURUS. [Apr. 1, 



The lumbar plexus (fig. 5) is remarkably simple, even more so 

 than in Erethizon dorsatus l ; it is formed from the last three lum- 

 bar (the fifth, sixth, and seventh lumbar nerves) and the first sacral ; 

 as in E. dorsatus there is no connexion between the nerve from 

 which the crural and obturator nerves are derived and the anterior 

 root of the great sciatic ; the anterior crural nerve (a.c) is formed 

 by the junction of the fifth and sixth lumbar nerves, from which also 

 the obturator nerve (ob) is given off; the great sciatic (s) is formed 

 by the last (the seventh) lumbar nerve and the first sacral only. In 

 the distribution of the nerves of this plexus no peculiarities are 

 noticeable. 



To sum up, C. melanurus, while differing so remarkably from 

 C. pilorides in the absence of that subdivision of the hepatic lobes 

 which has been described in the latter species 2 , and in the presence 

 of two pre-caval veins, resembles it closely in other respects in its 

 visceral anatomy, and probably also in its myology, as the few 

 notes available on the myology of C. pilorides agree with the writer's 

 observations on that of ft melanurus. In their general anatomy 

 both species show the close relationship which exists between this 

 genus of Octodonlidce and the genera of Hystricida, indicating the 

 near affinities of these two families of Hystricine Rodents. 



EXPLANATION OF PLATES. 



Plate XVIII. 



Capromys melanurus, half natural size. 



Plates XIX. & XX. 



Fig. 1, 1 a. Liver of C. melanurus, showing convex and concave surfaces. 



2,2 a. Liver of C. pilorides, showing corresponding surfaces, c, Caudate 

 lobe ; g, gall-bladder ; I, suspensory ligament ; l.c, left central 

 lobe ; l.l-l.V ', left lateral lobe ; r.c, right central lobe ; r.l, right 

 lateral lobe ; s, spigelian lobe. 



Plate XXI. 



Fig. 1. Stomach of C. melanurus (natural size), dorsal surface, c.c, Cardiac 

 cul-de-sac ; d, duodenum ; oz, oesophagus ; py, pylorus. 



2. Caecum, half natural size, co, colon ; i, ilium. 



3. Proximal part of ca3cura (three fourths natural size) laid open, 



showing the ileo-ciecal valve (c), and the position of the two 

 patches (a, a') of agminated glands ; i, ileum ; co, colon. 



4. Uterus and upper half of vagina, the latter (v), the os uteri (0. u), 



and part of the right and left cornua {c, c') are laid open ; on either 

 side the mesometrium (m) with vessels, the ovaries (pv.), the open 

 peritoneal capsules (cp) each traversed by the Rillopian tube {fp), 

 and the ostium (indicated by a bristle, b) of the latter opening on 

 the outer border of the peritoneal capsule, are shown. 



1 Mivart, P. Z. S. 1S82, p. 281, fig. 9. 



2 It is therefore evident that the subdivided condition of the hepatic lobes 

 into lobeiets can no longer be considered characteristic of the genus Capromys. 



