A Contribution to tlic Anafomy of Siren Inrertina. 657 



4. Lig.aiiiüiitum i n ter mu s eu la re mediale. 



This thin and unimportant ligament occupies the median line 

 from a protuberance upon the occipital region, as far forward as the 

 nose. It forms a wall of sei)aration between the muscles of the two 

 opposite sides. 



5, Fascia digastrici. 



This extremely dense fascia is formed of two ligauients, the posterior 

 and lateral intermuscular. It invests the outer surface of the anterior 

 portion of the digastricus and at its anterior border protects the ju- 

 gular and mandibular nerves. 



m. Muscles. 

 1 . Massctcr (p e t r o - 1 y m p a n o - m a x i 1 1 a r i s) (figs. 1 , 3 m, in, ni"). 



Preparation. This is the very large, oval, bipenniform muscle, 

 which covers the exterior posterior half of the dorsal surface of the 

 head. It is readily recognized by its tendon, which traverses the 

 longer axis of the oval, and collects the fibres. 



As the majority of the branches of N e r v u s trigeminus lie 

 in its vicinity, its dissection must be cojiducted with especial care; 

 and is best done in the following way: 



1) Carefully separate this muscle, without cutting, from the Liga- 

 mentum intermusculare anterius, which lies between it and the tem- 

 poralis. This separates the anterior interior border of the muscle. 

 Several branches of the trigeminus nerve will be seen lying between 

 the two muscles. 2) In a similar way, free the exterior l)order from 

 the M. digastricus. 3) Commencing at the posterior end of this last 

 line of separation, cut away the origin of the muscle, working in 

 a medial direction and keeping close to the bone. When this is ac- 

 complished, fold the muscle over anteriorly, and notice: a) The sur- 

 face of bone exposed, b) The second and third portions of the same 

 muscle lying deeply and inmediately in front of Os alisphenoidale, 

 c) A branch of Ramus maxillae inferioris trigemini, which passes out 

 between the two deep-lying muscles, supplying them before issuing. 



Origin. Pars prim a arises 1) from the external surfaces of 

 the three Ligamenta intermuscularia, anterius, mediale and posterius ; 

 and from the superior surface of Ligamentum intermusculare laterale. 

 2) From the posterior two-thirds of the dorsal surface of Os parietale, 

 from the entire dorsal surface of the tympanic and quadrate bones 

 as well as from the dorsal surfaces of the wedge-shaped anterior 

 portion of Os petrosum and the cartilaginous alisphenoid. 



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