208 THE ANATOMY OF THE HORSE. 



the artery here being remarkable in that it is actually within a 

 vein. 



At the inferior end of the sinus the vidian nerve will be found descend- 

 ing in the vidian groove to enter the canal of the same name (page 214). 



The Rectus Capitis Anticus Major. This muscle was, for the most 

 part of its extent, exposed in the dissection of the neck, but its tendon 

 of insertion remains to be examined now (page 155). 



The Rectus Capitis Anticus Minor. This small muscle arises from 

 the lower aspect of the ring of the atlas ; and passing over the occipito- 

 atlantal joint, at the side of the preceding muscle, it becomes inserted 

 into the basilar process of the occipital and the body of the sphenoid at 

 their point of articulation. 



Action. — To flex the occipito-atlautal joint (to nod the head). 



The Rectus Capitis Lateralis. This is another small muscle placed 

 beneath the occipito-atlantal joint. It arises from the atlas, external to 

 the origin of the preceding muscle ; and passes to be inserted into the 

 styloid process of the occipital bone. 



Action. — The same as the preceding muscle. 



the orbit. 



Directions. — With the saw, cut through the supraorbital process 

 external to the foramen, and through the zygomatic arch at either 

 extremity. The palpebral ligament of the upper lid is to be detached 

 from the orbital rim, and the tri-radiate piece of bone marked out by 

 these sections is to be taken away. 



The orbital cavity in the skeleton is not separated from the temporal 

 fossa, but in the living animal a fibrous membrane, continuous with the 

 periosteum of the bones circumscribing the cavity, completes the orbit 

 on its outer side, and separates it from the temporal fossa. The orbit 

 is thus lined and completed by a fibrous membrane of a conical form, 

 termed the ocular sheath. This membrane is composed of fibrous con- 

 nective-tissue with some unstriped muscular fibre. 



Contents of the Orbital Cavity. — These are : the eyeball with its 

 muscles, the lachrymal gland, the levator palpebral, the membrana 

 nictitans, vessels, nerves, and a quantity of fat. For the pi'oper dissec- 

 tion of the eyeball, fresh specimens are required, and it is therefore 

 separately described at page 257. The lachrymal gland and the 

 muscles may be dissected on one side, the other being reserved for the 

 display of the vessels and nerves. 



The Lachrymal Gland is the organ which secretes the watery fluid 

 that moistens the front of the eye. It is lodged above the eye, beneath 

 the supraorbital process, which is slightly depressed where it covers the 

 gland. In structure it is of the racemose type, resembling the salivary 

 glands, but being looser in texture. Its secretion is discharged by a 



