52 SPECIAL ANATOMY. 



convolutions of the brain and the Pacchionian glands, the Sulci arteriosi (for 

 Arteria meningea anterior) ; in the central line : crista frontaKs internet, the 

 commencement of the sulcus longitudinalis (for sinus long, superior), and foramen 

 ccEcum, a blindj sometimes open hole (for fulx cerebri). 



Conjunctions : above with the Parietal bones, below with the great wings 

 of the Sphenoid, laterally with the malar bones. 



b. Paries orbitales, orbital portions, horizontal, the superior walls of the 

 orbits, separated by the Incisura ethmoidalis, in which the Ethmoid lies. 



1. Inferior surface, triangular, concave, in the orbit. Towards the nose ; 

 fossa or spina trochlearis (for muse, obliq. superior) externally fovea lacrymalis 



(for the lacrymal gland). 



2. Superior surface, convex, uneven, in the cranial cavity, supporting the 

 inferior surface of the anterior cerebral lobes. 



3. Borders. The internal forms with the annexed Ethmoid bone, foramina 

 ethmoidalia (for Nerv. Art. et Ven. ethmoid.}, and lies anteriorly upon the Lacry- 

 mal bone ; the external unites with the malar bone, laterally ; with the great 

 wing of the Sphenoid, behind. 



c. Pars nasalis, nasal portion, short, thick, immediately below the Glabella, 

 between the orbital portions, beneath excavated in a horse-shoe shape into an 

 Incisura nasalis with a projecting spine, spina nasalis (for the nasal bones and 

 upper jaw-s), on the sides of which are the openings of the frontal cavities, 

 sinus frontaks. 



The frontal sinuses, only completely developed after the age of 

 puberty, lie between the two tables of the frontal portion, from 

 the inferior margin of which they ascend to the frontal eminences ; 

 they are divided by a septum into two, sometimes several unequal 

 spaces, and open with the anterior ethmoidal cells immediately 

 below the middle nasal turbinate bone. They are lined with 

 periosteum and ciliated epithelium. 



Development. It begins in the second month of foetal life with two lateral 

 centres of ossification, in the arcus superciliaris, which in the first year are 

 associated by a suture (sutura frontalis), which for some years continues dimi- 

 nishing. It sometimes exists during the whole life. The cavities appear in 

 the first year, and by degrees enlarge even up to old age. 



b. The cranial bones occurring in pairs. 

 51. 5. Ossa parietalia, s. bregmatis, vertex bone. 



Two quadrangular, flat, externally convex, internally concave 

 bones ; broader before than behind ; united together by the sagit- 

 tal suture; forming the highest part of the cranial vault; one on 

 either side of the central line, two surfaces, four borders, four 

 angles. 



Surfaces : 



1. External, convex, smooth, vaulted in the centre, tuber parietale, the centre 

 of ossification ; terminal point of the greatest transverse diameter ; below 

 this the linea semicircularis, the concave boundary line of the planum 

 semicircularis, which is above convex (for the muse. temp, and fascia tem- 

 poral). 



