QUESTIONS AND ANSWERS 95 



membrane. It serves to maintain the convexity of the cornea and 

 assists in refracting the rays of light. 



Describe the Eustachian tube and state its function. 



The Eustachian tube is a fibrocartilaginous canal, about four 

 inches long, extending from the middle ear to the pharynx. Its 

 upper orifice is narrow, but the inferior is widened by a great slit, 

 the borders of which are cartilaginous in structure. Its inferior 

 border is cleft, allowing the mucous membrane to escape in the form 

 of a large sac, known as the guttural pouch. It is bordered by the 

 stylopharyngeus muscle. 



Function : maintains the equilibrium of air within the cavity of 

 the tympanum. 



Describe the membrana tympani. 



The membrani tympani, or ear-drum, is a thin membrane which 

 separates the middle ear from the auditory canal ; oval in shape and 

 is attached by its circumference to a bony frame, the tympanitic 

 circle. Its inner face is slightly convex and is adherent to the 

 handle of the malleus. Although very thin, it consists of three 

 layers, a middle fibrous and muscular, an external of skin, and an 

 internal of mucous membrane. 



The function of this drum-like membrane is to receive the vibra- 

 tions of the sound waves and transmit them to the internal ear. 



Skin, Haie and Hoof 



Name the appendages of the skin. 



Hair, sweat-glands, sebaceous glands and horny parts (chest- 

 nut, ergot and hoof and, in ruminants, horns). 



Describe the different structures that make up the elastic cushion of 

 the heel. 



These consist of two fibroeartilages and the plantar cushion. 



The cartilages, two in number, are flattened plates, shaped like 

 an oblique-angled parallelogram. They are attached in front to 

 the anterior lateral ligament, behind to the basilar and retrossal 

 processes and plantar cushion ; they have a thin upper border and 

 a thick lower. The upper border is notched for the passage of 

 vessels and nerves. 



The plantar cushion is a wedge-shaped mass, situated between 

 the lateral cartilages, the perforans tendon and the lower part of the 

 hoof. Superiorly, it lies against the expansion of the perforans 

 tendon and is attached by ligamentous bands to the ergot, meta- 

 carpus and OS pedis. Inferiorly, it is covered by the keratogenous 



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