^58 ^^'- HARRIS 11 WII.DER, 



Pars sec un da, the anterior of the two small portions, arises 

 from both lateral margins, the point, and the inferior surface of the 

 alisphenoid process. Fig. 3 m. 



Pars tertia arises from the anterior border and inferior sur- 

 face of the cartilaginous alisphenoid. This third portion is considerably 

 larger than the second, and has a very deep origin, the majority of 

 its fibres coming from beneath the margin of the alisphenoid. Fig. 3 m". 



Insertion. The three portions are inserted into the upper 

 margin of the lower jaw, beside one another, the insertion of the 

 I'' portion being the farthest forward, the 2"^ following, and the 

 3''' farthest back, immediately before the articulation. 



Innervation. The Ramus maxillae inferioris trigemini supplies 

 all portions, passing out, as stated above, between the 2"*^ and 

 3"* portions. 



Conclusions. The extreme amount of dift'ereutiation which 

 this muscle has gained, especially in so low an animal, is worthy of 

 remark. The two internal portions seem quite distinct from the ex- 

 ternal layer, and the innermost portion might readily admit of a farther 

 division into an internal and an external portion. It is quite possible 

 that here we meet with a separation of the pterygoids from the pri- 

 mitive mass of masticatory muscles, and that these two inner portions, 

 as well as the pterygo-maxillaris, described below, correspond to the 

 pterygoid, of higher Vertebrates. It may be noticed that the third 

 branch of the trigeminus runs between these portions, as between the 

 external and internal pterygoids in the human subject. 



2. Digastricus (cephalodorso-maxillaris) (figs. 1, 2 and 3 ôî, d'). 



Preparation. This muscle is the large oval mass lying upon 

 the side of the head between the masseter and the hyoid arches. It 

 is invested by a thick fascia which is a continuation of Ligamentum 

 intermusculare laterale, and which posteriorly becomes continuous with 

 Ligamentum intermusculare posterius. The muscle is to be exposed 

 by cutting through this investing fascia along the anterior border, 

 and drawing it backwards. Care must be taken, in cutting through 

 the fascia, not to harm the two posterior branches of Nervus facialis, 

 Rr. raandibularis et jugularis, which come from behind the muscle at its 

 anterior border, and run downwards and forwards along the ventral surface. 



After the removal of the fascia, the muscle will be seen to consist 

 of two portions, a smaller anterior portion from the skull, and a larger 

 posterior portion from the cerato-hyal 



