132 PROFESSOR OWEN ON THE ANATOMY OF 



tendon to that of the fellow muscle. The fleshy part forms a long slender band six 

 lines in breadth, which passes forward, and about four inches from its origin sends off a 

 slender fleshy strip (PI. XXXVII. fig. 2, x) to the ceratohyoideus, n, and the central 

 tendon, *. It then advances as a slender round fleshy muscle, which degenerates 

 into a subcompressed tendon about half an inch in length, opposite the compressor 

 salivaris. Resuming its fleshy structure, it forms an anterior subcompressed belly, ten 

 inches in length and from four to five lines in diameter (PI. XXXIX. fig. 1, w). This 

 gradually contracts and terminates in a slender tendon three inches long, which ex- 

 pands to be inserted into the outer and under part of the maxillary ramus, six inches 

 in advance of the angle of the jaw. 



To the action of the pair of muscles, so inserted, is mainly due that characteristic 

 movement of the head of the Great Anteater when it composes itself to sleep, and draws 

 its head downward and backward between the fore-limbs, in contact with the chest. 

 The mouth is small, and susceptible of so slight an opening as not to require for that 

 action so remarkable a modification of what appears to be a dismemberment of the 

 homologue of the sternocleidomastoideus muscle. 



The proper muscles of the jaws consist of the temporalis, the masseter, and the 

 pterygoidei. 



The temporalis (PI. XXXIX. fig. 2, a) arises from a low ridge extending from the stunted 

 zygomatic procesis of the squamosal upwards and slightly forwards, — the boundary rather 

 of a large and ill- defined orbit than of a temporal fossa, which is in no wise marked off 

 from the orbit : some fibres are derived from the temporal fascia ; but the muscle is 

 not above an inch in breadth, and its greatest length does not exceed an inch and a 

 half; it is inserted into the external ridge, an inch in advance of the condyle, which 

 feebly represents a coronoid process. 



The masseter (PI. XXXIX. figs. 1 & 2, 6) has an extent of origin of three inclies three 

 lines from the malar process of the maxillary, from the short and free malar, and from 

 a very strong fascia continued thence over the temporal muscle to the zygomatic pro- 

 cess of the squamosal. The maxillary origin has the appearance of a distinct tendon, b' , 

 expanding into an aponeurosis, which spreads over nearly the upper half of the outside 

 of the muscle. The carneous fibres from the maxillary tendon pass vertically down- 

 ward : the more posterior fibres proceed more obliquely downward and backward as 

 they approach the angle of Ihe jaw, into which the most posterior ones are inserted. 

 The extent of the insertion from this point forward is four mches two lines. The 

 action of this muscle is to close the mouth and protract the mandible. 



The pterygoideus inlernus arises, chiefly fleshy, from a longitudinal channel on the 

 under part of the pterygoid bone, which is bounded mesially by a low ridge, to which a 

 short aponeurotic origin of the muscle is attached : the muscle gains in thickness and 

 depth as it passes forward and outward to be inserted into the concavity on the inner 

 side of the ascending articular part of the jaw. 



