198 



REPORT — 1846. 



inconstant, its functions being transferred in many mammals to another pro- 

 cess, sometimes urlcler-shaped, sometimes of great length (fig. 24, 4), but 

 which is developed from the exoccipital, and is represented in the human skull 

 by the ' eminentia aspera,' &c. of Soemmerring (Table I. 4), and by the "sca- 

 brous ridge extended from the middle of the condyle towards the root of the 

 mastoid process" of Munro (op. cit. p. 72) ; but sometimes also here deve- 

 loped, as a rare anomaly, on one or both sides, into a process like a second 

 but smaller posterior mastoid*. The more constant and essential characters 

 of the mastoid are its contribution to the walls of the acoustic chamber, 

 carried to anchylosis with the petrosal in birds and mammals, and its sutural 

 connection in the latter with the exoccipital, parietal, and squamosal (the 

 squamo-mastoid suture becoming obliterated in many species, e. g. the hog, 

 fig. 24, 8, 27) : it is also grooved, notched or perforated by a greater or less 

 proportion of the lateral venous sinus, whether this is continued to the ' fora- 

 men jugulare,' as in man, or sends a large division to escape by the ' meatus 

 temporalis ' which forms the large orifice between the mastoid and squamosal 

 above the meatus auditorius in the horse and ruminants, and which directly 

 perforates the mastoid in the echidna (fig. 12, m). 



Fig. 12. 



16'0=' 



Partially disarticulated cranium of the Echidna setosa. Natural size, 



It is important to keep these essential characters steadily in view,and to avoid 

 giving undue importance to the apophysial character of the mastoid, which has 

 led to so common a transference of its name, in the great osteological works of 

 Cuvier and De Blainville, to a quite distinct element (paroccipital) of the 

 cranial wallsy. It is necessary, also, to be prepared for that change of the 



* The continuators of Cuvier make mention of an example of this kind and propose the name 

 of ' paramastoid ' for the process (Legons d'Anat. Comp. ii. (1837) p. 312). I have observed 

 it in the skull of a New Zealander and in that of an Irishman, preserved in the Museum of 

 Anatomy in Richmond Street, Duhlin. Believing it to be the homologue of the ' paroccipital ' 

 (4), which is developed independently in chelonia and most fishes, I retain that name for it : 

 it must not be confounded with that angle of the occipital which projects into the ' foramen 

 jugulare ' in the human skull, and which has received the name of ' processus jugularis,' in 

 some systems of anthropotomy. 



f How essential a correct view of special homology becomes to the appreciation of the 



