390 PROCEEDINGS OF THE ACADEMY OF [1880. 



of the lower border of the Bialar bone, the entire lower border of 

 the enormous infra-orbital foramen. Its insertion is not only 

 npon the angle but the median surface of the ramus as well. The 

 last-named insertion occurs as follows : The anterior edge of the 

 muscle becomes stout and broad as it approaches the rounded 

 border of the bone in front of the angle. It winds round this 

 border, receiving as it does so a large accession from the angle, 

 and a portion of the adjacent median surface from the lower jaw. 

 This portion of the masseter lies below the jaw on the soft parts 

 of the neck. In addition to the above, a long, stout, fusiform 

 belly is inserted b}' fleshy fibres at a point half way up the ramus 

 in front, and above the upper border of the insertion of the in- 

 ternal pterygoid muscle. 



Beneath the superficial fibres just described, the masseter in 

 Erethizon exhibits the usual tendinous fibres arising from the 

 angle and passing upward and forward. The third set is of great 

 importance in this animal. It agrees with the general plan of 

 arrangement in other mammals examined, but is remarkable for 

 its extent. It arises from the lower and median border of the 

 zygoma by tendinous fibres, from the side of the maxilla, at the 

 nasal region and supra-orbital surface of the same bone- by fleshy 

 slips, also fleshy from the upper concave border of the zygoma, 

 where fibres form the supra-zygomatic slip ; tendinous and fleshy 

 from the anterior and lower half of the inner wall of the orbit. 

 The insertion of this set of fibres is upon the ramus, between the 

 angle and the sigmoid notch. The anterior part of the insertion 

 is rounded and tendinous. It lies beneath the corresponding 

 border of the surperficial portion, and receives the fibres passing- 

 through the infra-orbital foramen. The remaining portions unite 

 to be inserted as already indicated. 



The temporal muscle possesses a superficial portion, which 

 everywhere covers in the main muscle. Its aponeurosis arises 

 from the vertex, the upper border of the posterior half of the 

 orbit and the posterior and upper half of the inner wall of the 

 same depression. It thus covers in the post-orbital process of 

 the frontal bone. It is inserted entirely upon the main tendon, 

 and receives no fasiculus from the masseter. The deep or main 

 portion extends its aponeurosis forward, to be inserted stoutl}- 

 upon the post orbital process of the frontal bone. A thin apo- 

 neurosis passes downward, thence to the mandible behind the 

 coronoid. 



