PEOFESSOE OWEN ON MACEOPUS. 419 



concave lengthwise, through the descent of a postglenoid process (ib. figs. 1, 5, pff), in- 

 ternal to which is a perforation. 



The alisphenoid (ib. fig. 3, ir) sends down a process (ib. fig. 1, 6') abutting against 

 the par occipital (4). The three compartments of the cranial cavity — epencephalic, 

 prosencephalic, and rhinencephalic — succeed each other lengthwise ' ; and the olfactory 

 cavity extends backward both above and beneath the rhinencephalic fossa. The "sella 

 turcica " is indicated by the entocarotid foramina ^, not by clinoid processes. The basi- 

 occipital (ib. fig. 3, 1 ) is hexagonal, the hind border emarginate, forming the lower 

 fourth of that of the foramen magnum (ib. fig. 4, 0) and contributing a very small part 

 to each condyle (g). The ex occipital (ib. fig. 4, 2) develops the rest of that joint- 

 surface (g), which is oblong-convex, with an upper or back portion bent at a right angle 

 to the rest of the convexity. In young Macropodidee the superoccipital (ib. fig. 4, 3) 

 contributes a small share to the upper border of the foramen, which extends thereto by 

 a fissure-like prolongation upward, between the then separate occipitals. These, 

 however, by subsequent growth contract the fissure, and in adults of some large species 

 obliterate it and complete the foramen by the exclusion of the superoccipital. There 

 are two or more precondyloid foramina (ib. fig. 3, p), anterior to which is the vagal 

 foramen (v), and next the larger single jugular notch (u), through which may be seen 

 the hind end of the petrosal (le) ; this notch is usually completed, as a foramen, by the 

 paroccipital process of the alisphenoid 6', anterior to which the fore part of the petrosal 

 is visible ; but in some the union with the exoccipital (ib. 2-6) does not take place, 

 and the whole extent of the basal part of the petrosal is seen ; the junction of the ali- 

 sphenoid (ib. fig. 1,6') with the paroccipital (ib. 4 ) is constant and extensive. A smooth 

 channel curves round the upper part of the condyle (ib. fig. 4, g) between it and the 

 base of the paroccipital (4). The superoccipital (ib. fig. 4, 3) is octagonal, the upper 

 and lower borders being the shortest ; the lateral ones next these above and below are 

 the longest ; the two outer sides are of intermediate extent. There are two rough 

 oblong depressions (ib. 3, x) near the upper lateral borders, for tendinous attachments. 

 Superiorly the superoccipital joins the interparietal (ib. fig. 2, 3), varying in shape and 

 composition; laterally it joins the parietal (7) and mastoid ( 8 ), and in some species 



' The relative positions of the rhinencephalic, prosencephalic, and epencephalic compartments of the cranium 

 are the same in lissencephalous (see Osteol. Collection, Mus. Coll. Chir. Sections nos. 2165, 2292, 2337, 2391, 

 2407) as in lyencephalous Mammals ; the compartment for the rhinencephala (" olfactory ganglions " or 

 " hulbs " of anthropotomy), which compartment Prof. Flower terms " olfactory fossa," is as much in front of 

 the prosencephalic compartment or " cerebral fossa " in the Beaver and Agouti (no. 2051) as in the Wombat 

 or Kangaroo. " The ' olfactory chambers ' attain their maximum of development in some of the Porcupines 

 {Hystrix):" Flower, Osteol. of Mammalia, 12mo, p. 153. Here the author means the fossae appropriated to 

 the olfactory sense-organ. Those which lodge the divisions of the brain supplying the nerves of that organ, I 

 had termed, to avoid confusion, " rhinencephalic." 



" Osteol. Catal. 4to, 18.53, p. 323, no. 1735 ; this character is common to the order, see Art. " Marsupialia," 

 Cycl. of Anat. (1847), p. 274. 



3l2 



