The septomaxillary.—The septomaxillary (spmax., [Fig. 9a-c]) is a triradiate bone. The anterior terminus is a thin sliver of bone oriented horizontally between the cavum principale and cavum medium and lateral to the lamina superior ([Figs. 5] [and 8a]). This anterior ramus of the septomaxillary increases in size posteriorly and diverges medially into a medial ramus (med. r. spmax.) and lateral ramus (lat. r. spmax., [Fig. 9a-b]) to accommodate the confluence of the cavum principale and cavum medium ([Figs. 6] [and 8b-c]). The small medial ramus is associated with the distal end of the lamina superior whereas the lateral ramus lies dorsal to the lateral margin of the cavum medium. Just anterior to the anterior end of the nasolacrimal duct, the ventral ramus of the septomaxillary (vent. r. spmax., [Fig. 9c]) is present in cross-sections ventral to the cavum medium. The ventral ramus joins the horizontal and dorsal rami of the septomaxillary at the anterior end of the nasolacrimal duct. The medial branch terminates posteriorly at the level at which the cavum principale joins the cavum inferior. The lateral ramus of the septomaxillary terminates posteriorly at the level at which the recessus medialis diverges from the recessus lateralis posteriorly and cavum principale and recessus lateralis are confluent.
Planum terminale.—Posterior to the infundibulum the lamina inferior and oblique cartilage join to form the planum terminale (pla. term.) which lies lateral to the cavum principale ([Fig. 10]). The lamina inferior diverges ventrally from the planum terminale anterior to the olfactory eminence. The planum terminale is restricted ventrally and terminates at the level of the olfactory eminence (olf. em., [Fig. 11]).
Fig. 8. Transverse sections through olfactory capsule in region of septomaxillary: a) anterior terminus of septomaxillary; b) medial divergence of septomaxillary; c) dorsal ramus of septomaxillary; d) posterolateral terminus of septomaxillary. Encircled numbers represent the nasal cavities as follows: 1) cavum principale; 2) cavum medium; and 3) cavum inferius. Abbreviations: al. c., alary cartilage; ant. spmax., anterior end of septomaxillary; cr. int., crista intermedia; dor. r. spmax., dorsal ramus of septomaxillary; ext. nar., external nares; inf. pnas. c., inferior prenasal cartilage; l. inf., lamina inferior; l. sup., lamina superior; lat. r. spmax., lateral ramus of septomaxillary; med. r. spmax., medial ramus of septomaxillary; nas., nasal; nlc. dt., nasolacrimal duct; obl. c., oblique cartilage; pvom., prevomer; sept. nas., septum nasi; sol. nas., solum nasi; spmax., septomaxillary; tect. nas., tectum nasi.
Fig. 9. Septomaxillary drawn from cleared and stained specimen of Smilisca baudini, KU 55614: a) dorsal; b) ventral; c) lateral. In each example, the anterior end lies to the left. Abbreviations: dor. r. spmax., dorsal ramus of septomaxillary; lat. r. spmax., lateral ramus of septomaxillary; med. r. spmax., medial ramus of septomaxillary; vent. r. spmax., ventral ramus of septomaxillary.