THE HEAD. 



front, and at an advanced age is found in a plane passing by the inferior 

 extremity of the zygomatic crest and the summit of the external occipital 

 tuberosity. 



2. If the cranium be examined by itself, it will be noted that, in proportion, 

 it is less narrowed behind the orbital processes in the young animal than in the 

 adult. With regard to the cerebellar cranium, it is elongated when the animal 

 is aged — a consequence of the natural development of the external occipital 

 tuberosity. 



3. The relation of the areas of the cranium and face change with age. If 

 the measurements obtained by Colin on the Lamb and Ram are compared, it 

 will be perceived that the face grows as the creature ages. This change is very 

 evident if the development of the young Hare is watched. At birth the face is 

 very short — like that of a common dog, it is said ; but when development is 

 completed, we know how much the face has become lengthened. 



4. Finally, in consulting the table of angles drawn up by Colin, we might 

 believe that the facial angle widens as the animal advances in age. Thus, in the 

 young Hinny, Colin estunated the facial angle at 15° ; this angle was 16° on an 



Fig. 53. 



A, B, C, D. 1, Fronto-parietal crests; 2, external occipital tuberosity; 3, 3, superior root of 

 the zygomatic process of the temporal bone. 



old Hinny, and 17° on another very old one. In every instance, however, according 

 to the same table, this angle will be equal in a four-years-old Horse and in an 

 adult Horse ; and even in the Calf it diminishes one degree when it becomes an 

 adult animal. 



The measurements we have taken in domestic Solipeds, have demonstrated 

 that the facial angle diminishes in a constant manner as the animal grows old. 

 Thus, this angle is 16° in an Ass three years old ; it is 15° in the adult, and 12° 

 in the very old Ass. We have found it 13° in a Foal of two years, and 11° in 

 an old Horse ; 15° in a Mule of eighteen months, and 12*30° in a very aged 

 Mule. 



This question has, therefore, to be again examined ; and, however it may be 

 decided, it will be seen, by what has been stated, that age induces very interesting 

 changes in the form and proportions of various parts of the head. 



If the crania of different breeds of Dogs are compared, there will be found 

 very marked diversities in the prominence of the parietal convexity, and the 

 development and distance apart of the fronto-parietal crests. A mere glance 

 at the ligures above (Fig. 53), will afford evidence of this. 



