60 THE SKELETON OF THE HORSE 
deep sphenoidal notch (Incisura sphenoidalis), which is closed by the orbital wing 
of the sphenoid. — Its lateral surface forms part of the inner wall of the temporal 
fossa. ‘The medial surface is largely covered by the orbital wing of the sphenoid 
in the young subject, but later forms part of the wall of the frontal sinus. 
The principal connections of the frontal bone are as follows: (1) The medial 
border joins its fellow at the frontal suture. (2) The anterior border meets the 
nasal and lacrimal at the naso-frontal and fronto-lacrimal sutures. (3) Laterally 
it forms the spheno-frontal suture with the orbital wing of the sphenoid, and also 
joins the palatine bone and maxilla at the fronto-palatine and fronto-maxillary 
sutures. (4) Posteriorly it meets the parietal at the parieto-frontal suture, and 
articulates below this with the squamous temporal at the squamous suture. 
(5) The extremity of the supraorbital process unites with the zygomatic process 
of the temporal bone. 
Development.— Each ossifies in membrane from one center which appears in 
the root of the supraorbital process. In the new-born foal there is a slit between 
the cranial plate and the orbital and temporal plates which receives the unossified 
dorsal part of the orbital wing of the sphenoid. 
THE TEMPORAL BONES 
The temporal bone (Os temporale) forms the greater part of the lateral wall 
of the cranium. It is situated between the occipital behind, the parietal dorsally, 
the frontal in front, and the sphenoid ventrally. It consists in the horse of two 
distinct parts, squamous and petrous. 
1. The squamous temporal bone (Squama temporalis) is a shell-like plate 
which has two surfaces and four borders. 
The cerebral surface (Facies cerebralis) is concave and is largely overlapped 
by the surrounding bones, but its central part is free and presents digital impres- 
sions and vascular grooves. 
The temporal surface (Facies temporalis) is convex, and enters into the forma- 
tion of the temporal fossa. From its ventral part there springs the zygomatic 
process (Processus zygomaticus), which forms the lateral boundary of the tem- 
poral fossa. The process is at first directed outward, and is wide and flattened 
dorso-ventrally. It then turns forward, becomes narrower, and is twisted so that 
its surfaces are medial and lateral. Its anterior end is pointed and joins the zygo- 
matic process of the malar bone, with which it forms the zygomatic arch (Arcus 
zygomaticus). The narrow anterior part has a convex lateral surface and a concave 
medial one. Its dorsal border has a rough area for articulation with the supra- 
orbital process of the frontal. Its ventral border is wide and rough. The wide 
posterior part presents on its ventral face a surface for articulation with the condyle 
of the mandible. This surface consists of a transversely elongated condyle (Condy- 
lus temporalis), behind which is the glenoid cavity. The fossa is limited behind by 
the postglenoid process (Processus postglenoidalis), the anterior surface of which 
is articular. Behind this process there is a fossa, in which is the postglenoid fora- 
men (I. postglenoidale), the external opening of the temporal canal. The dorsal 
surface is concave and forms the lateral boundary of the temporal fossa. The 
dorsal border is sinuous and is continuous behind with the temporal crest. 
The posterior process (Processus aboralis) springs from the posterior part of 
the squama. Its lateral surface bears the temporal crest, which forms here the 
lateral limit of the temporal fossa. The medial surface forms the outer boundary 
of the temporal canal, and is elsewhere applied to the petrous portion. It divides 
into two branches, upper and lower; the upper branch unites with the occipital 
bone, while the lower one curves downward behind the external acoustic process 
and overlaps the mastoid process. 
The dorsal border of the squamous temporal articulates with the parietal, 
