392 MR. G. E. DOBSON ON THE [Mar. 1, 



the zygoma and the margin of the orbit. All four muscles form 

 very long and slender tendons, which pass forward horizontally 

 parallel to one another, to be inserted respectively into the upper 

 lip, slightly in front of the first upper incisor, into the extremity of 

 the nose below the nasal orifice, into the middle of the alae nasi, 

 and into the extremity of the nose above the nasal orifice. Between 

 the origins of the zygomaticus major and minor arises another 

 muscle, the levator labii superioris et erector vibrissarum, which 

 passes directly forwards between the tendons of these muscles, and 

 terminates in a mass of muscular fibres which invest the bases of 

 the remarkably long vibrissse which spring from the sides of the 

 muzzle, and is also connected with the orbicularis oris beneath. 

 The levator labii superioris proprius is well developed, arising from 

 the maxillary bone above, and in front of the infraorbital foramen, 

 forming a strong tendon, which, united over the extremity of the 

 muzzle with the tendon of the corresponding muscle of the opposite 

 side (as in Equus), is inserted with it into the upper lip below the 

 nasal orifices. 



The temporal muscle is remarkable for its great size and peculiar 

 development. It arises by three heads, which are all inserted into 

 the coronoid process : — 



I. From the greatly developed occipital crest and surface of the 

 parietal bones, in the usual position of origin, inserted into the 

 superior and anterior margin of the coronoid process. 



II. From the mastoid process, root and upper margin of the 

 zygoma along its posterior two thirds, the fibres curve upwards, 

 forwards, and downwards, forming a semicircular muscular mass 

 above the zygoma on the side of the head, lying against the tem- 

 poral muscle proper ; inserted into the outer side of the coronoid 

 process near its base. 



III. From the inner side of the posterior two thirds of the 

 zygomatic arch a mass of muscular fibres arises, which, curving 

 forwards, is inserted into the postero-external margin of the upper 

 half of the coronoid process. 



We have thus a series of muscular structures having an exceed- 

 ingly extended origin, and of great relative development, attached to 

 the much-expanded coronoid process of the mandible, supplying the 

 force needed to move such greatly extended jaws ; for, probably, in 

 no other mammal are these so much developed in comparison with 

 the size of the animal. 



Not less remarkable in its development is the digastric. This 

 muscle ^arises normally ; but at the point where the tendinous in- 

 tersection occurs (nearly opposite the hyoid bone) it splits iuto 

 two laminse : one, superficial and external, continues forward in 

 the usual direction of the muscle ; the other, transverse, is di- 

 rected inwards, and slightly forwards, its posterior free tendinous 

 margin being a direct continuation of the tendinous intersection 

 of the muscle, which unites in the middle line in front of the 

 hyoid bone with that of the corresponding muscle of the opposite 

 side, forming a tendinous raphe, from which the united muscles are 



