A Contribution to the Anatomy of Siren lacertina. 6()1 



Insertion. Both portions unite to form a common tendon, 

 which IS inserted into the coronary process of the mandible. 



Innervation. From Ramus maxillae inferioris trigemini by 

 several small branches which are given otf soon after the exit of 

 the nerve from the cranium. 



(;, piNote. For the description of M. pterygo - maxillaris which pro- 

 perly belongs to this system, see the end of the section upon the 

 muscles. 



4. Iiitermaxillaris anterior (mylo-hyoideus) (figs. 1, 4i.m.a.). 



Preparation. The animal is now to be turned upon its back, 

 exposing the broad, ventral surface of the head and throat. A trans- 

 verse muscular layer reaching across the intermaxillary space and 

 extending posteriorly to a Une drawn between the second pair of ex- 

 ternal gills, is composed of this and the following muscle, which at 

 first sight seem scarcely separable from one another. 



A more complete scrutiny will detect a difference in the direction 

 of the fibres, while laterally, at the boundary between them, is formed 

 a triangular space, in which lies the pterygo-maxillaris. 



The anterior muscle is to be separated from the posterior at this 

 boundary, divided near the median line, and turned back. 



Origin and Insertion. The fibres of this muscle arise from 

 the entire internal border of the mandible on both sides and are in- 

 serted into a tendinous raphe in the median line. 



Innervation. The nerve supply comes from the large recur- 

 rent muscular branch of Ramus maxillae inferioris trigemini, which 

 divides and sends one portion through the mandible, between Meckel's 

 cartilage and the dentale, thus reaching the muscle. The nerve, after 

 its passage through the bone, lies upon the muscle, and supplies it 

 in its course. 



5. Intermaxillaris posterior (stylo-hyoideus) (figs. 1,4/. m. p.). 



Preparation. After noting from the outside the way in which 

 the most posterior fibres of this muscle lie upon the cerato-hyoideus 

 externus, the muscle may be divided in the middle line and turned back. 



Origin. Commencing from the most posterior, its fibres arise: 

 1) from the anterior surface of the 1'^ epibranchial, 2) from the fascia 

 covering the cerato-hyoideus externus, 3) from the anterior surface of 

 the cerato-hyal, 4) a few fibres take their origin from the fascia 

 Ibetween the cerato-hyal and the mandible. 



