748 



THE SENSE ORGANS AND SKIN OF THE HORSE 



parts (crura helicis). The posterior border is convex. The apex is flattened, 

 pointed, and curved a Httle forward. The base is strongly convex. It is attached 

 to the external auditory process of the petrous temporal bone, and around this there 

 is a quantity of fat. The parotid gland overlaps it below and externally. The 

 structure of the external ear comprises a framework of cartilages (which are chiefly 

 elastic), the integument, and a comiilicated arrangement of muscles. 



The conchal or auricular cartilage (C'artilago auricuke) determines the shape 

 of the ear; its form can be made out without dissection, except below, where it is 

 concealed by the muscles and the parotid gland. The l)asal part is coiled to form 

 a tube, which incloses the cavity of the concha (Cavum conchse). This part is 

 fvumel-shaped and curves outward and a little backward. Its internal (medial) 

 surface is strongly convex, forming a prominence termed the eminentia conchae. 

 The lowest part of the internal margin bears a narrow, pointed prolongation, the 



styloid process. This process is 

 about an inch long and projects 

 downward externally over the an- 

 nular cartilage; the guttural pouch 

 is attached to its free end. Behind 

 its 1)ase there is a foramen through 

 ^j" which the auricular branch of the 



vagus passes. 



The basal part of the posterior border 

 is cut into by a notch, which separates two 

 irregular quadrilateral plates. The upper 

 plate (Tragus) is overlapped by the an- 

 terior border, and is separated from the 

 adjacent part of the posterior border 

 (Antitragus) by a notch (Incisura inter- 

 tragica). The lower plate is curved to 

 form a half ring and partly overlaps the 

 anterior border and the annular cartilage. 

 \ Behind the notch there is a foramen, 



\ which transmits the internal auricular 

 artery and internal auricular branch of 

 the facial nerve. 



Fig. 562. — Conch.\l and Annular Cartilages of Ear of 

 HoR.sE, External View. 



i, Base of concha; .2, posterior bortler, .-i, anterior bor- 

 der of concha; Jt, intertragic notch; 5, eminentia conchse; 

 6, styloid process; 7, annular cartilage; 9, zygomatic arch. 

 (After Ellenberger-Baum, Anat. fiir Kunstler.) 



The annular cartilage (Cartil- 

 ago annularis) is a quadrilateral 

 plate, ctu'ved to form about three- 

 fourths of a ring; its ends are a 

 little less than half an inch (ca. 

 1 cm.) apart internally and are 

 united by elastic tissue. It em- 

 braces the external auditory process and forms with the lower part of the conchal 

 cartilage the cartilaginous part of the external auditory canal. 



The scutiform cartilage (C'artilago scutiformis s. scuttilum) is an irregular 

 quadrilateral plate which lies on the temporal muscle in front of the base of' the 

 conchal cartilage. Its superficial face is slightly convex from side to side and its 

 deep face is correspondingly concave. The anterior end is thin and rounded; the 

 posterior part or base is wider and thicker, and its inner angle is prolonged by a 

 pointed process half an inch or more in length. The cartilage moves very freely 

 over the underlying parts. 



The external auditory canal or meatus leads from the cavum conchse to the 

 tympanic meml)ran('. It does not continue the general direction of the cavity of 

 the concha, but extends inward, downward, and slightly forward. It consists of a 

 cartilaginous part formed by the lower part of the conchal cartilage and the annular 

 cartilage, and an osseous part formed by the external auditory process of the tern- 



