554 



BLOOD-VASCULAR SYSTEM OF THE HORSE 



periorbita along the outer edge of the levator palpebrse superioris to the lacrimal 

 gland, in whicli it is chiefly distriljuted. It also sends twigs to the upper eyelid. 



(c) Muscular branches (Rami musculares) suj^ply the orbital muscles, the 

 periorbita, the third eyelid, and the conjunctiva. 



(d) Ciliary branches (Aa. ciliares), two sets of very slender arteries, arise 

 from the ophthalmic direct and from the muscular branches. The anterior ciliary 

 arteries (Aa. ciliaries anteriores) pierce the sclera in front of the equator and ramify 

 chiefl}^ in the ciliary body and the iris. The posterior ciliary arteries (Aa. ciliares 

 posteriores) pierce the posterior part of the sclera; most of them ramify in the 

 choroid coat as the short ciliary arteries, but two of larger size, the long ciliary 



Fig. 440. — Sagittal Section of Head of Horse, Cut a Little to the Right of the Median Plane. 

 1, Skin; 2, nasal bone; 3, frontal bone; 4, parietal bone; 4', tentorium osseum; 5, occipital bone; 6, 

 sphenoid bone; 7, hard palate; 8, premaxilla; 9, mandible; 10, hyoid bone; 11, septum between frontal sinuses; 

 1£, alar cartilage; 13, dilatator naris transversus; 14, septum nasi with venous plexuses, 16, palato-labial artery; 

 16, 16', upper and lower sei^tal branches of 15; 17, septal branch of sjjhenopalatine artery and satellite vein; 

 IS, septal branch of ethmoidal artery; 19, sphenoidal sinus; £0, guttural pouch; 21, pharynx; 22, pharyngeal 

 orifice of Eustachian tube; 23, posterior naris; 24, soft palate; 25, palatinus muscle; 26, pharyngeal muscles; 

 27, oesophagus; 28, dotted line indicating position of posterior pillar of soft palate; 29, lamina; 29' , arch of cricoid 

 cartilage; SO, arytenoideus transversvis muscle; 31, epiglottis; 32, body of thyroid cartilage; 33, vocal process 

 and cord; S^, arytenoid cartilage; iio, lateral ventricle of larynx; 36, trachea; .:?7, ventral straight muscles of head; 

 38, longus colli; 39, atlas; 40, axis; 41, hg- nuchse; 4^, dorsal spinal muscles; 43, muscles of external ear; 44< 

 omo- and sterno-hyoideus; 45, tongue; .4^, mylo-hyoideus; 4^', genio-hyoideus; 4'?, genio-glossus; -$9, longitudinalis 

 inferior; 60, longitud. superior; 61 , hyo-epiglotticus; 62, chin and mentalis muscle; 63, venous plexus of hard 

 palate; 64, corpus callosum; 65, sejitum jjellucidum; 66, fornix; 67, thalamus; 68, pineal body; 69, corpora 

 quadrigemina; 60, cerebral peduncle; 61, corijus mammillare; 62, pituitary body; 63, chiasma opticum; G4, inter- 

 carotid artery; 65, medulla oblongata; 66, interventricular foramen; 67, infundibulum; 68, third ventricle; 69, 

 cerebral atjueduct; 70, anterior medullary velum; 71, fourth ventricle; 72, posterior medullary velum; 73, basilar 

 artery; 74, spinal cord; 75, ethmoidal nerve; 7G, septal branch of posterior nasal nerve; 76', branch of same to 

 organ of .lacobson; 77, olfactory nerve to organ of Jacobson; 78, nasal branches of palatine artery. (After Ellen- 

 berger, in Leisering's Atlas.) 



arteries, run forward, on(^ on each side, between the sclera and choroid to the 

 periphery of the iris. Here they divide into branches which anastomose and form 

 a circle (Circulus iridis major). From this secondary branches are detached which 

 form a second circle around the pupil (Circulus iridis minor). 



(e) The central artery of the retina (Arteria centralis retinae) is a small vessel 

 which arises from tiie ()])hthalini(' or from a posterior ciliary artery. It pierces the 

 optic nerve a short distance behind the sclera and runs in its center to the lamina 

 cribrosa, where it breaks up in thirty to forty fine branches. These appear in 

 the fundus of the eye at the margin of the optic papilla and radiate in the posterior 

 part of the retina. 



(/) The ethmoidal artery (A. ethmoidalis) is the continuation of the oph- 



