href="@public@vhost@g@gutenberg@html@files@34233@[email protected]#Fig_2_5" class="pginternal" tag="{http://www.w3.org/1999/xhtml}a">Fig. 3) along the posterior surface of the alary process and then curves posterodorsally and joins the solum nasi medioventral to the posterior end of the septomaxillary (Fig. 8d).

Tectum nasi.—The anterolateral corner of the tectum nasi (tect. nas., Fig. 2) appears just posterior and dorsomedial to the anterior end of the alary cartilage. The anterior process is short; it fuses medially with the septum nasi forming a complete roof to the cavum principale (Figs. 3 and 4). The oblique cartilage (obl. c.) diverges laterally from the tectum nasi just posterior to the terminus of the alary cartilage (Fig. 6). Medially, the tectum nasi persists, overlaid by the nasal bone laterally.

Septum nasi.—Posterior to the appearance of the septum nasi (sept, nas.) and its union with the tectum nasi (Fig. 3), the septum abruptly expands across the width of the skull medial to the alary cartilage. The septum is entirely cartilaginous posterior to the level of the olfactory eminence, except for a small amount of secondary membranous ossification dorsomedially at a level anterior to the nasal bones. Perichondral ossification commences in the dorsal part of the septum nasi at the level of the olfactory eminence. Endochondral ossification first appears dorsally in the vertical part of the septum at the level of the internal nares. Ossification of dorsal parts of the septum precedes ossification of ventral parts. Perichondral ossification of the ventral part of the septum nasi is first noted at the level of transition between the planum antorbitale and solum nasi. Perichondral ossification gradually gives way to endochondral ossification posteriorly.

Nasal cavities and associated structures.—The cavum principale (cav. prin., Fig. 4) is the most anterior of the nasal cavities. It first appears within the capsule bordered dorsally by the tectum nasi, medially and ventrally by the septum nasi, and laterally by the alary cartilage. The cavity extends posteriorly within recesses of the sphenethmoid to the level at which the septum nasi terminates.

The cavum medium (cav. med., Fig. 5) lies ventral and slightly posterior to the anterior end of the cavum principale. It appears slightly anterior to the septomaxillary at the level of the foramen ramus externus narium and ramus medialis narium. The appearance of the cavum medium within the ventrolateral extension of the septum nasi divides the latter into an upper component, the lamina superior (l. sup.) lying between the cavum principale and cavum medium, and a lower part, the lamina inferior (l. inf.) lying ventral to the cavum medium. As the cavum medium increases in width in posterior sections, the lamina superior and lamina inferior lose their lateral connection. The lateral part of the cavum medium diverges in the region of the external nares as the nasolacrimal duct (ncl. dt.) and the cavum medium becomes confluent with the cavum principale (public@vhost@g@gutenberg@html@files@34233@[email protected]#Fig_6_7" class="pginternal"