116 



TBE BONES. 



obliquely truncated behind, from the summit to the base. It offers for study : 

 three faces, three borders, and two lateral angles. 



Faces. — The anterior, convex from side to side, and cribbled by porosities and 

 vascular openings, shows on each side : 1. The preplantar fissvre — a horizontal 

 groove more or less ramified, which commences behind, between the retrossal and 

 basilar processes, terminating in front in one of the foramina that penetrate 

 the bone. 2. The patilohe eminence — a roughened projecting surface, situated 

 between the preceding fissure and the inferior border of the bone. The superior 

 face is occupied by an articular surface formed by two glenoid cavities and a slight 

 median ridge ; it comes in apposition with the inferior face of the second phalanx. 

 The inferior (or solar) face, hollowed out like an arch, is divided into two regions 



by the semilunar crest, a salient line which describes 

 a curve forwards. The anterior region is perforated 

 with very fine porosities, and corresponds to that part 

 of the hoof named the sole. The posterior region 

 shows, immediately behind the semilunar crest, a 

 median imprint, and two lateral channels designated 

 the plantar fissures. These originate at the root of 

 the basilar process, are directed obliquely downwards 

 and inwards, and open into th.Q plantar foramina, 

 the external orifices of two large canals which enter 

 the bone and unite in its interior to form the semilunar 



Y\z. 74. 



PLA.NrAR SURF.\CE OF THIRD 

 PHALANX. 



1, Lower face, or sole ; 2, 3, 

 wings, or retrossal pro- 

 cesses ; 4, internal border ; 

 5, plantar foramina. 



Sinus. 



Borders. — The superior describes a curve, with 

 the convexity forward, and presents : 1. In its middle, 

 the pyramidal eminence of the os pedis— a single tri- 

 angular process, flat before and behind, roughened on its anterior aspect, and 

 concurring, by its posterior surface, to form the articular surface which responds 

 to that of the second phalanx. 2. Laterally, two facets of insertion which 

 encroach on the anterior surface, and even advance, posteriorly, nearly to the 

 preplantar fissure. The inferior border is thin, dentated, convex, and semicir- 

 cular ; it is perforated by from five to ten large foramina, which pass into the 

 bone. The posterior border is slightly concave ; on it is observed a very narrow, 

 transversely elongated, diarthrodial facet, which becomes confounded with the 

 superior large articular surface, and is adapted to a similar facet on the navicular 

 bone. 



Lateral angles. — These are two projections directed backwards, on the summit 

 of which the three borders of the bone unite, and which gives attachment to the 

 lateral fibro-cartilages. A deep notch — the origin of the preplantar fissures — 

 separates each into two particular eminences : one, the superior, named by 

 Bouley the basilar jrrocess ; the other, the inferior, prolonged behind, and desig- 

 nated by Bracy Clark the retrossal process (from retro, behind, and ossa, bone). 



Structure. — The os pedis exhibits in its interior the semilunar sinus — a cylin- 

 drical, transversely elongated, and semicircular cavity resulting from the arching 

 anastomoses of the two plantar canals. From this cavity pass off numerous 

 channels, which anastomose frequently with each other, and open externally by 

 the foramina on the anterior face of the bone, or by those on its inferior border. 



The OS pedis has for its base a nucleus of spongy substance, surrounded by a 

 layer of compact tissue. The latter is thicker towards the pyramidal eminence 

 than elsewhere, and sends into the interior numerous prolongations which form 



