MUSTELUS L^VIS. 175 



of the peri-orbital sinus is called by Kidewood (54), in 

 Scyllium, the post-orbital blood-sinus. Here tbo trigeminal 

 nerve leaves the truncus facialis and turns laterally and 

 backward across, and dorsal to, the anterior portion of the 

 anterior diverticulum of Wright's (70) descriptions of the 

 spiracular cleft of the fish. It has Iiere already separated 

 into three parts — one larger and two smaller ones, — all of 

 which pass outward anterior to the superior postspiracular 

 ligament of Ridewood's descriptions of Scyllium, and anterior 

 also to the posterior or auditory diverticulum of the spiracular 

 cleft. One of the smaller parts of the nerve was here lost 

 in the sections. The other two parts both reach the internal 

 surface of the levator maxillai superioris muscle of Vetter's 

 descriptions, which they seem to penetrate and innervate. 

 A part of the fibres of the nerve are, howevei-, quite un- 

 questionably distributed to the general tissues of the region, 

 for that the nerve contains general sensory fibres is clearly 

 shown by the two branches that arise from near its base, and 

 that accompany the two buccalis branches. 



The levator maxilUc superioris muscle of my embryo is 

 apparently exactly such a muscle as Tiesing describes in the 

 adult. 'J'lie muscles of my embryo that represent the three 

 muscles of the adult considered by Tiesing as parts of Csdj, 

 differ somewhat from those muscles as described by him, 

 but I should state that I am unable to clearly comprehend 

 his descriptions and figure of them. The muscle called by 

 Tiesing the levator palpebne nictitantis I find exactly as 

 he describes it, excepting that, as this muscle crosses the 

 two other muscles, dorsal to the spiracle, its postero-veutral 

 edge is imbedded in those muscles to such an extent that the 

 ventral half of its outer and inner surfaces is covered by 

 them. In transverse sections the levator muscle is here of 

 oval section, inclining towards the skull, the other two 

 muscles together forming, in sections, a deep gutter Avhich 

 encloses the lower half of the levator. The other two 

 muscles together form a T-shaped muscle, more or less 

 fused with the levator maxillae superioris. The T is placed 



