HEAD AND NECK OF THE HORSE 125 



corticalis) that gradually merges into the much denser nucleus or 

 central part (nucleus lentis). A hardened lens should be broken and 

 teased in order to show the concentric disposition of lamince and the 

 fibres that compose them. 



Between the cornea and the iris and central part of the lens there is 

 a space known as the a/nterior chamher of the eye (camera oculi 

 anterior). In the angle formed by the cornea and the iris, the angulus 

 iridis, the aqueous humour finds its way into the spatia anguli iridis. 

 The jposterior chamber of the eye (camera oculi posterior) is the circular 

 interval bounded by the iris, the suspensory ligament, the peripheral 

 part of the anterior surface of the lens and the projection formed by 

 the extremities of the ciliary processes. The anterior and posterior 

 chambers are filled with the aqueous humour, and communicate with 

 each other through the pupil. 



Dissection. — The blood-vessels and nerves that lie immediately below 

 the orbit, that is, in the pterygo-palatine fossa, must be cleaned and 

 examined. 



V. REFLEXA. — The reflex vein, which communicates anteriorly with 

 the facial, has previously been traced under the masseter muscle and 

 between the mandible and the maxillary tuber into the pterygo- 

 palatine fossa (page 49). In the present dissection it is seen to pierce 

 the periorbita and enter the cranium by the orbital fissure. The con- 

 nection of the vein with the cavernous venous sinus within the cranium 

 will be revealed at a later stage of the dissection. The following are its 

 tributaries : — 



(1) V. palatina major. — The greater palatine vein drains the blood 

 from the hard palate, where its radicles spring from an exceedingly rich 

 submucous plexus, and is now found between the maxillary tuber and 

 the perpendicular part of the palatine bone, where it is joined by veins 

 from the soft palate. It should be noted that the vein, inasmuch as it 

 does not traverse the palatine canal, is not a close companion of the 

 artery of the same name. 



(2) V. sphenopalatina. — The spheno-palatine vein begins in a rich 

 plexus of vessels in the mucous membrane of the nasal cavity, and gains 

 the pterygo-palatine fossa by the spheno-palatine foramen. 



(3) V. infraorbitalis. — The infraorbital vein, after traversing the 

 infraorbital canal, generally joins the reflex in company with the 

 spheno-palatine vein. 



(4) V. ophthalmica. — The short ophthalmic vein is formed by the 

 union of the ethmoidal, ciliary, muscular and lachrymal veins and the 

 central vein of the retina. 



