EQUTJS CABALLUS. 159 



below the carpus in the fore-foot r , are the same ; but those in the hind 

 are much stronger ; and there is a ' perforatus,' and a ' perforans :' the 

 perforatus makes a kind of theca or annular ligament for the perforans. 



The joint between the tibia and astragalus is such that the bones will 

 not remain in the half flexed state, but will jerk either to the extended 

 or the flexed state : [its movement] therefore requires an action of both 

 the flexors and extensors at the same time, although one is to give up 

 to the other, alternately 2 . 



The larynx lies at the lower part of the angle of the lower jaw which 

 is about the middle of the head ; from thence it passes up in the direc- 

 tion of the head towards the vertebras. 



The attachment of the pharynx to the basis of the head is 5 inches 

 from the foramen magnum occipitale, and where this attachment is, 

 there are the openings of the Eustachian tube. These openings are 

 placed laterally, and appear to be slits with the side towards the 

 pharynx-cartilage. At its beginning it [Eustachian canal and aperture] 

 is a foramen, but only for a quarter of an inch ; afterwards it is a 

 groove passing upwards and a little outwards, becoming shallower and 

 narrower: on the outside of this groove are the circumflex muscles, 

 and the cartilages are continued up to the bony part on the inside. 



Between the two Eustachian tubes is a cavity that leads up for 3 

 inches, the sides of which are the inner sides of the tubes, which makes 

 the tube a groove, on to the bony part, where it is a foramen ; in this 

 [part] there is a large cavity just above the turn of the larynx, the 

 boundaries of which are these : downwards, the oesophagus ; forwards, 

 the basis of the skull ; inwards, by a septum that divides it from the one 

 on the other side ; outwards, by the os hyoides [stylohyal] ; above, by 

 the pterygoideus internus ; between these two last by a membrane that 

 is on the inside of the condyle of the jaw ; and upwards by the recti 

 capitis muscles. This cavity is very irregular, having a process running 

 backwards and outwards towards the external ear, between it and the 

 condyle. The septum is connected forwards to the cavity between the 

 two Eustachian tubes. 



To conceive the course of all these parts it must be considered that 



1 [Hunt. Prep. No. 279. The structure of the hoof is shown in No. 284. The 

 structure and development of the teeth are shown in Nos. 333 — 379.] 



2 [In the Preparation, No. 257, ' Physiological Series,' Mus. Coll. Chir., Hunter 

 shows the " strong transverse ligament which passes from the head of one rib, behind 

 the intervertebral substance, to the head of the opposite rib ; thus connecting them 

 firmly to each other and to the vertebra."— Physiol. Catal. 4to. vol. i. (1832) p. 57. 

 See ' On a peculiar ligament connecting the opposite ribs in certain Vertebrate, ' by 

 Dr. Cleland, communicated by Prof. Goodsir to the Eoyal Society of Edinburgh, 

 'Proceedings,' April 1858, p. 101.] 



