. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. .336 ANATOMY OP VERTEBRATES. 219 of the globe. In the circular palpebral fold is deeper, and is provided with a sphincter : in most Scomberoid and Clupeoid Fishes there is an anterior and a posterior vertical trans- parent fold or eyelid. In the eye of the tope and blue Shark, there is a nictitating membrane superadded to a well-developed circular palpebral fold of the skin. A conjunctive membrane is reflected from the circular eyelid over the third eyelid, which is placed at the nasal side of the orbit,
. On the anatomy of vertebrates. Vertebrates; Anatomy, Comparative; 1866. .336 ANATOMY OP VERTEBRATES. 219 of the globe. In the circular palpebral fold is deeper, and is provided with a sphincter : in most Scomberoid and Clupeoid Fishes there is an anterior and a posterior vertical trans- parent fold or eyelid. In the eye of the tope and blue Shark, there is a nictitating membrane superadded to a well-developed circular palpebral fold of the skin. A conjunctive membrane is reflected from the circular eyelid over the third eyelid, which is placed at the nasal side of the orbit, and then passes over the anterior half of the eyeball. A strong' nictitator' mus- cle rises from the temjwral side of the orbit, and passing through a muscular and ligamentous loop, descends obliquely to be inserted into the lower margin of the third lid. The trochlear muscle has an insertion into the upper part of the circular lid, and depresses that part siuuil- taneously with the raising of the third lid.' The jiroper muscles of the eyeball exist in all fishes except the Myxinoids and Lepidosireu, and consist of the four recti, fig. 219,1,2,3,4, and two oliliqui, ib. «, h : the latter rise from the nasal side of the orbit, and are inserted most favour- ably for eflPecting the rotatory movements of the eyeball: but the superior oblique, a, has not its direction changed by a trochlea in the 2)rcsent class. In the Gahnis there is a special ])rotuberance of the upper part of the carti- laginous sclerotic for the common insertion of the rectus siiperior and obliqiD/s superior; and a second protuberance below for the c<:iniinon insertion of the ohliquus infer/or and rectus inferior. The recti muscles rise in many Osseous Fishes from the sub-cranial canal; '^ the origin of the rectus being prolonged furthest liack. But the recti muscles are most remarkable for their length in the Hammer-headed Sharks, since they rise from the basis cranii, and extend ak)ng the latera
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