1910.] The Hyracoidea. 361 



resembled the remote ancestors of those other orders, at least in its "]ioten- 

 tial of evolution." 



A very comjjrehensive description f)f the chief characters of the Hyra- 

 coidea is given bv Weber (1904, j). 707) so that what follows is merely an 

 analysis of the more important characters. 



A few of the pecidiaritieft of the Hf/racoidea which distiiujuish thnn from. 

 all other iingiilcite,s and point to a lone/ phi/logenetlc independence are as 

 follows: The proximal end of the colon gives ofi' a pair of coecal diverticida 

 which are unknown in other mammals; the arrangement of the cerebral 

 sulci is peculiar (Weber, 1904, p. 710) and likewise many of the details of 

 the vascidar and reproductive systems. 



The skeleton too abounds in specialized characters, some of which are 

 unicpie. A process from the parietal reinforces the postorbital process of 

 the frontal; the malar extends backward into the o-lenoid fossa; The hvoid 

 arch is "unlike that of any other mannnal" (Flower and Lydekker); the 

 scapula is V-shaped and lacks the acromion; the slender himierus has lost 

 the entepicondylar foramen; the clavicle is lost; the radius and ulna tend to 

 ankvlose, likewise the tibia with the proximal end of the fibula; the third 

 trochanter of the femur is reduced; the inner side of the astragalus has a 

 deep step like articulation for the tibial malleolus; the dorso lumbar formula 

 of D. 20-21 + L 7-9 is much higher than in any other primitive mammal ; the 

 number of sacrals, 5-7, is also very high, while the caudals are reduced to 4-8, 

 facts suggesting that the sacrum has been pushed back^vard along the caudal 

 series. 



Resemhlances to members of other orders. 



The above mentioned mixture of characters in Hyrax is well illustrated 

 in the characters of the eye as viewed under the ophthalmoscope. Accord- 

 ing to Lindsay Johnson (1901) the fundus oculi of Hi/rax retains two 

 marked and presumably primitive features in common with Rodents and 

 Marsupials: viz., it presents an aster-like radiation of nerve fibres and the 

 pale reddish brown fundus shows traces of choroid vessels. On the other 

 hand it shows a general resemblance to the fundi both of the Elephants and 

 of the Perissodactyls, since it has a large round disc, a uniform field with 

 bacillarv markings and small radiatino; retinal vessels. Finallv the fundus 

 of Ili/ra.v resembles that of the Artiodactyls in the development of a pro- 

 jection from the iris, the umbracidinn, which is highly contractile and serves 

 to screen the iris from strong light. Similarly also in regard to the arrange- 

 ment of the azygos veins Beddard (1907, p. 219) speaks as follows: " . . . . 

 the position and number of these veins in Hyrax are of particular interest. 

 In this 'subungulate,' admittedly primitive, and standing nearer to the 



